Role of inflammatory cytokines in depression: Focus on interleukin-1β

Neuroimmune Biomarkers in Mental Illness

Exploration of neuroimmune mechanisms is vital to the understanding of the pathogenesis and pathophysiology of mental disorders. Inflammatory and immune mechanisms are increasingly understood to underpin a number of neuropsychiatric disorders, with an ever-expanding evidence base drawn from basic science to large-scale epidemiological data. Unravelling of these mechanisms should lead to biomarker discovery and potential new avenues for therapeutics that modulate immunological mechanisms. Identification of neuroimmune biomarkers is vital to improving diagnosis, stratification and treatment of mental disorders. There is an urgent clinical need for new therapeutic approaches with poor treatment response and treatment resistance a major problem for many psychiatric disorders including depression and schizophrenia. Neurodegenerative psychiatric disorders such as Alzheimer's also have clear neuroimmune underpinnings and manifest an urgent clinical need for improvements in diagnosis and research towards transformative disease-modifying treatments. This chapter provides some background on the role of the neuroimmune system in mental illness, exploring the role for biomarkers, in addition to reviewing the current state of knowledge in this exciting field. We also reflect on the inherent challenges and methodological pitfalls faced by research in this field, including the complexity of conceptualising multidimensional mental disorders and the dynamic shifting sands of the immune system.

BICAO-induced ischaemia caused depressive-like behaviours and caspase-8/-9-dependent brain regional neural cell apoptosis in mice

Introduction

Cerebral ischaemia-induced depression is among the most frequent neuropsychiatric consequences and adversely impact the prognosis and recovery of patients. Although several brain regions have been implied in the development of ischaemia-induced depression, the brain region-specific neural cell apoptosis pathways have not been clarified yet.

Methods

In this study, bilateral internal carotid artery occlusion (BICAO) mouse model was established to induce cerebral ischaemia. Sucrose preference, tail suspension and forced swim tests were conducted on mice at 7, 21 and 30 days after BICAO treatment. In addition, brain regional ischaemic neuron loss was investigated by using immunofluorescent staining of neuronal nuclei (NeuN) and caspase-8/-9-dependent cell apoptosis was also examined by western blot analysis.

Results

BICAO-induced cerebral ischaemia resulted in decreased sucrose preference and increased immobility times, which were representative depressive-like behaviours of mice until 30 days after BICAO treatment compared with Sham-operated mice. This outcome was associated with significant neuron loss by using immunofluorescent staining and increased cleavage levels of pro-caspase-3/-8/-9, but not pro-caspase-12, by western blot analysis in hypothalamus, midbrain, prefrontal cortex and hippocampus of mice.

Conclusions

This study showed that BICAO-induced ischaemia caused depressive-like behaviours and caspase-8/-9-dependent neural cell apoptosis in several brain regions, including hypothalamus and midbrain of mice.

Lentivirus-mediated interleukin-1β (IL-1β) knock-down in the hippocampus alleviates lipopolysaccharide (LPS)-induced memory deficits and anxiety- and depression-like behaviors in mice

Background

Recent evidence has suggested that peripheral inflammatory responses induced by lipopolysaccharides (LPS) play an important role in neuropsychiatric dysfunction in rodents. Interleukin-1β (IL-1β), a pro-inflammatory cytokine, has been proposed to be a key mediator in a variety of behavioral dysfunction induced by LPS in mice. Thus, inhibition of IL-1β may have a therapeutic benefit in the treatment of neuropsychiatric disorders. However, the precise underlying mechanism of knock-down of IL-1β in repairing behavioral changes by LPS remains unclear.

Methods

The mice were treated with either IL-1β shRNA lentivirus or non-silencing shRNA control (NS shRNA) lentivirus by microinjection into the dentate gyrus (DG) regions of the hippocampus. After 7 days of recovery, LPS (1 mg/kg, i.p.) or saline was administered. The behavioral task for memory deficits was conducted in mice by the novel object recognition test (NORT), the anxiety-like behaviors were evaluated by the elevated zero maze (EZM), and the depression-like behaviors were examined by the sucrose preference test (SPT) and the forced swimming test (FST). Furthermore, the levels of malondialdehyde (MDA), superoxide dismutase (SOD), nuclear factor erythroid-derived 2-like 2 (Nrf2), heme oxygenase 1 (HO1), IL-1β, tumor necrosis factor (TNF-α), neuropeptide VGF (non-acronymic), and brain-derived neurotrophic factor (BDNF) were assayed.

Results

Our results demonstrated that IL-1β knock-down in the hippocampus significantly attenuated the memory deficits and anxiety- and depression-like behaviors induced by LPS in mice. In addition, IL-1β knock-down ameliorated the oxidative and neuroinflammatory responses and abolished the downregulation of VGF and BDNF induced by LPS.

Conclusions

Collectively, our findings suggest that IL-1β is necessary for the oxidative and neuroinflammatory responses produced by LPS and offers a novel drug target in the IL-1β/oxidative/neuroinflammatory/neurotrophic pathway for treating neuropsychiatric disorders that are closely associated with neuroinflammation, oxidative stress, and the downregulation of VGF and BDNF.

Biomarkers for depression: recent insights, current challenges and future prospects

A plethora of research has implicated hundreds of putative biomarkers for depression, but has not yet fully elucidated their roles in depressive illness or established what is abnormal in which patients and how biologic information can be used to enhance diagnosis, treatment and prognosis. This lack of progress is partially due to the nature and heterogeneity of depression, in conjunction with methodological heterogeneity within the research literature and the large array of biomarkers with potential, the expression of which often varies according to many factors. We review the available literature, which indicates that markers involved in inflammatory, neurotrophic and metabolic processes, as well as neurotransmitter and neuroendocrine system components, represent highly promising candidates. These may be measured through genetic and epigenetic, transcriptomic and proteomic, metabolomic and neuroimaging assessments. The use of novel approaches and systematic research programs is now required to determine whether, and which, biomarkers can be used to predict response to treatment, stratify patients to specific treatments and develop targets for new interventions. We conclude that there is much promise for reducing the burden of depression through further developing and expanding these research avenues.